Rename the Firebase consumer keep rules file

The -dontwarn is still required: firebase-messaging ships no consumer rules and
we exclude firebase-analytics from its dependencies. Only rename the file to
consumer-rules.keep and reword the comment, which embedded a local path.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

libraries/pushproviders/firebase/build.gradle.kts

@@ -26,10 +26,10 @@ android {
 
     buildTypes {
         getByName("release") {
-            consumerProguardFiles("consumer-proguard-rules.pro")
+            consumerProguardFiles("consumer-rules.keep")
         }
         register("nightly") {
-            consumerProguardFiles("consumer-proguard-rules.pro")
+            consumerProguardFiles("consumer-rules.keep")
             matchingFallbacks += listOf("release")
         }
     }